AKRON, Ohio -- A decade ago a dozen major tire manufacturers, half of them U.S. companies, vied for world leadership.

Now six giant companies are dominant. Goodyear Tire & Rubber Co. is the only one based in the United States.

Consolidation has come about because of slackening demand and the challenges of global competition. With long-lasting radials now accounting for 93 percent of new passenger vehicle tires, motorists buy fewer replacements.

Weak demand has forced companies to invade each other`s territories. And as the auto industry becomes more global, automakers favor huge tire companies that can fill their needs.

In the past five years, foreign companies have bought out most of the best-known U.S. labels, including Firestone, General, Armstrong, Uniroyal and Goodrich.

In addition to Goodyear, only the smaller Cooper Tire Co. remains independent in the United States.

The agreement five months ago by Groupe Michelin of France to buy the Uniroyal Goodrich Tire Co. creates the largest tire manufacturer if U.S. antitrust regulators approve.

Goodyear, which had been the leader for decades, is contending for second place with the Bridgestone Corp. of Japan, which two years ago bought Firestone.

Next come West German Continental AG, which bought General Tire; Pirelli SPA of Italy, which owns Armstrong; and the Sumitomo Tire and Rubber Co. of Japan, which bought Dunlop.

Two smaller Japanese makers, the Yokohoma Rubber Co. and the Toyo Tire & Rubber Co., are concentrated in the Far East.

Consolidation has intensified competition to cut production costs and increase quality.

The industry has become surprisingly high-tech, spending more than $1 billion on research and development last year, up by one-third from five years ago.

At Goodyear`s vast research and development center in Akron, the rubber meets the microchip before it meets the road.

Rows of technicians at computer workstations design tires.

They test them with computer programs that seem like video games. On screen, cars whip through courses with potholes, ice slicks and hairpin turns.

A decade ago, designing a tire for a new automobile model required testing 200 to 300 tires. Today, it takes about 65.

``In the last few years, tire designing has moved from an empirical art to a science, because of the computer,`` said F. Vincent Prus, Goodyear`s executive vice president for research and development.

The major tire companies are spending freely, 2.5 percent to 3 percent of revenues, on research and development.